Switching circuit for operation and dynamic braking of a dc motor

ABSTRACT

A switching circuit for controlling the operation of a DC motor or the dynamic braking of the motor, having driving circuits for selectively driving the motor in different directions when selectively connected to a direct current source and having dynamic braking circuits for connection to the motor armature winding, which dynamic braking circuits include solid-state switching devices which respond to a directional coasting of an undriven armature to complete a dynamic braking circuit to dynamically brake the motor. The dynamic braking-circuit switching devices are inhibited by means included in the driving circuits from completing the dynamic braking circuit while the motor is being driven.

United States Patent [72] Inventor Arthur J. Edhlund 3,378,740 4/1968Cruel 318/380 T ofM i 3,463,991 8/l969 Yummaka et al 318/258 PP 822,200Primary Examiner-Otis L. Rader [22] Flled May 1969 Assistant Examiner-K.L. Crosson [45] Patemed 1971 Attorney-Kinney, Alexander, Sell, Steldtand Delahunt [73] Assignee Minnesota Mining and Manufacturing CompanySaint Paul, Minn.

[54] N AND ABSTRACT: A switching circuit for controlling the operation 2Claims, 1 Drawing FM of a DC motor or the dynamic braking of the motor,having driving circuits for selectively driving the motor 1n differentU.S. direction when selectively connected to a direct current 313/261,318/380 source and having dynamic braking circuits for connection to[51] Int. Cl H02!) the motor armature winding which dynamic brakingcircuits ofSearch include olid-state witching devices which respond to a261, 379,380 directional coasting of an undriven armature to complete adynamic braking circuit to d namically brake the motor. The [56]eferences Cned dynamic braking-circuit swi t ching devices are inhibitedby UNITED STATES PATENTS means included in the driving circuits fromcompleting the 3,371,259 2/ 1968 James et al. 318/380 dynamic brakingcircuit while the motor is being driven.

SWTTCHING CIRCUIT FOR OPERATION AND DYNAMIC BRAKING OF A DC MOTORBACKGROUND OF THE INVENTION This invention relates to a switchingcircuit for a DC motor for selectively operating the motor in eitherdirection by reversing the armature voltage and including circuit meansfor providing a dynamic breaking circuit, such as a low impedance pathfor the current induced by the coasting armature when the drivingcircuit is open, such that the motor is dynamically braked to a stop.

The principle of dynamic braking-to-stop direct current motors byremoving applied voltage and providing a low impedance path for thecurrent induced in the coasting armature is well known. Inunidirectional applications the switching is also very straight forward.In applications however where it is desired to run the motor in eitherdirection, the prior art has resorted to cumbersome multicontactdual-polarity switches or relays or dual-polarity power supplies.

SUMMARY OF THE INVENTION The present invention affords a switchingcircuit, for selectively controlling a direct current motor includingdriving circuit for running the motor in a given direction and a dynamicbreaking circuit for dynamically'breaking the motor, wherein the dynamicbraking circuit is completed by switching means which are responsive toa directional coasting of an undriven armature.

In accordance with the present invention, it is possible to controldirect current motors to run in either direction and to be rapidlystopped without the cumbersome multicontact dual-polarity switches orrelays or dual-polarity power supplies utilized by the prior art.

The switching circuit of the present invention operates from a source ofdirect current. A pair of driving circuits are connected to eachterminal of a direct current motor for driving motor in one direction orthe other. Each of the driving circuits include switching means whichcomplete the circuit from one side of a DC source through the motor andback tothe source of direct current. Dynamic braking circuits aredisposed in generally parallel relationship with the armature terminalsof the motor to afford a closed loop current path for the armaturecurrent when the driving circuits are opened'to enable dynamic braking.

Each dynamic braking circuit includes switching means, the switchingmeans of one braking circuit being responsive to electrical energygenerated by the armature coasting in the forward direction forcompleting a current path across the armature, and the switching meansof the other dynamic braking circuit being similarly responsive toenergy generated by the armature coasting in the reverse direction.

BRIEF DESCRIPTION OF THE DRAWING The drawing illustrates a schematiccircuit diagram of the switching circuit constructed in accordance withthe present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT The motor switching circuit ofthe present invention is adapted to drive DC motors, having motor fieldmagnetic flux supplied by permanent magnets or energized field windings,in a manner to drive the motor in either direction and to brake themotor. The present invention provides the bidirectional switchingcircuit to drive the current through the armature winding in eitherdirection. The preferred switching means of the driving circuits and ofthe dynamic braking circuits are solid-state switching devices.

Referring to the drawing, a source of direct current 4, in the form of abattery, is connected through its two terminals to two leads and 6. Thelead 5 is connected to the single-pole terminal 7 of a single-poledouble-throw selector switch 8 having lead terminals 9 and 10 forforward and reverse positions respectively. The single-pole double-throwselector switch 8 atfords a means for energizing circuits to drive themotor 12 in either forward or reverse direction.

The switching circuit of the present invention includes a pair ofsymmetrical driving circuits each connected to a lead terminal of theswitch 8 and to an armature terminal of the motor for placing the DCvoltage across the armature winding to drive the motor in both forwardand reverse directions. To effectively drive the motor, of course, thedrive circuits must be closed back to the supply 4 through conductor 6.Switching means are included in the driving circuits such that in eitherthe forward or the reverse operating position of the switch 8' the motoris energized and the circuit is closed to the source of direct current.

Dynamic braking circuits which are disposed in generally parallelcircuit relationship to the armature winding of the motor are providedsuch that upon opening the switch 8 to a stop position after havingdriven the motor in either direction, the coasting armature will act asa generator providing an induced current which is conducted through adynamic braking circuit across the armature terminals to dynamicallybrake the motor.

To describe the circuit, assume that a motor 12 has permanent fieldmagnets and it is desired that the motor 12 run in the forward directionsuch as the direction of the arrow 13. The selector switch 8 is operatedto move the switch blade to make contact between pole 7 and terminal 9.A current path is thereby established from the power supply 4 throughthe conductor 5 through switch 8 and through a lead 14. Current is thensupplied through the diode 1'5, creating a voltage drop across diode 15.The voltage drop across the diode 15 places a reverse bias on thebase-emitter junction of a PNP transistor 17, thereby preventing currentflow through the transistor 17, thereby holding open the switching meansin a first braking circuit of which the transistor 17. is a part, aswill hereinafter be described, thereby inhibiting the operation of thisfirst dynamic braking circuit. The current pathv is continued from diode15 toward a first terminal 19 of the motor 12 through a first lead 21which has a junction ahead of the terminal 19 where the current divides.A major portion of the current passes through the armature winding ofthe motor 12 causing it to rotate in the forward direction 13, but aminor portion of the current moves through a branch circuit, whichincludes conductor 22, resistor 23, and a first driving circuitswitching means, NPN transistor 24. The current moves through conductor22 to the resistor 23 and through the base-emitter junction of the NPNtransistor 24; The current passing through the base-emitter junctionplaces the transistor 24 in conducting condition thereby permitting themajor portion of the current passing through the armature winding of themotor 12 to flow through the collector and the emitter of the transistor24 to the conductor 6, to close the circuit to the power source 4. Thisswitching means 24 is a part of the first driving circuit to drive themotor 12 in the forward direction 13. A similar symmetrical seconddriving circuit including switching means such as an NPN transistor 26completes a circuit through the lead terminal 10 of the switch 8 toarmature terminal 20 through the armature winding and from armatureterminal 19 through NPN transistor 26 and conductor 6 to the source todrive the motor 12 in the reverse direction, opposite to arrow 13, whenthe selector switch 8 is moved to the reverse position.

When it is desired to stop the armature from further rotation in theforward direction of the arrow 13, the switch 8 is opened to the stopposition, thereby breaking connection between the pole 7 and terminal 9.At that moment the power from the source is interrupted and the armaturecoasts due to its inertia, thus generating a voltage at the armatureterminals 19 and 20 of the same polarity as the voltage immediatelypreviously applied from the source but with opposite current flow. Thefirst dynamic braking circuit now provides a path for resistor 16 flowsthrough conductor ,6 to the anode of a diode I 27 to the terminal of themotor. The current from the emitter to base of the transistor l7.placesthe transistor 17 in conducting condition thereby allowing a currentflow from the annature terminal 19, through the lead 21, through theemitter and the collector of the transistor 17, and through a diode 28and a lead 29 directly to the terminal 20. The current path throughtransistor 17 (emitter to collector) and through the diode 28 provides alow impedance path for the armature current of the motor 12 as isrequired to afford effective dynamic braking. The braking effect iscontrolled by the value of the resistor 16 and the direct current gainof transistor 17. Diode 28 protects PNP transistor 17 from the effectsof collector to base reverse current.

in the preferred embodiment, the driving circuits and the dynamicbraking circuits are symmetrical. Therefore, the other half of theswitching circuit will not be described in detail as it would be merelyrepetitious.

In the preferred embodiment, the components are selected to have thefollowing listed identities and values for switching a Barber Colemanmodel BYQM 3267 DC motor rated at 24 volts and 100 ma. and havingan'armature winding having a re- I sistance of approximately 300 ohms.

Larger motors may be switched-and braked by using transistors and diodeshaving higher current ratings. The braking circuit switching means anddriving circuit switching means may be adapted for substitution of othersolid-state switching devices, such as thyristors, for the transistorsdescribed herein. 1

1. A switching circuit for selectively controlling the operationanddynamic braking of a direct current motor having first and secondarmature terminals, comprising:

a driving circuit for connectingjadirect current power source acrosssaid first and second armature terminals of said motor to drive saidmotor in a forward direction, which driving circuit comprisesj. I

a first diode having an anode for connection to a positive side of saiddirect current power source and a cathode for connection to said firstarmature terminal,

a NPN transistor having a collector for connection to said secondarmature terminal and an emitter for connection to a negative side ofsaid direct current power source,and i a resistor connected between thebase of the NPN transistor and the cathode of the first diode.

whereupon, when the first diode cathode is connected to said firstarmature terminal and the NPN transistor collector is connected tosaidsecond armature terminal and the NPN transistor emitter is connectedto said negative side of said direct current power source, theconnection of the first diode anode to said positive said of said directcurrent power source enables the NPN transistor to conduct therebycompleting the driving circuit to drive said motor in said forwarddirection, and

a dynamic braking circuit for connection across said armature terminalsof said motor to dynamically brake said driven motor upon the drivingcircuit being opened so that said armature is coasting. in said forwarddirection, which dynamic braking circuit comprises;

a PNP transistor having an emitter connected to the cathode of the firstdiode, having a base connected to the anode of the first diode, andhaving a collector operatively connected to the collector of the NPNtransistor.

a second diode having a cathode connected to the collector of the NPNtransistor, and

a second resistor connected between the base of the PNP transistor andthe anode of the second diode,

' whereupon, when the driving circuit is connected to said directcurrent power source and to said armature terminals and said motorisbeing driven in said forward direction, the opening of the drivingcircuit by disconnecting the anode of the first diode from said positiveside of said direct current power source to terminate conduction in theNPN transistor thereby causes the armature to coast in the forwarddirection to generate electrical energy and valso thereby enables thePNP transistor .to conduct in response to said generated electricalenergy to complete the dynamic braking circuit across said first andsecond armature terminals.

2. A switching circuit according toclaim l for selectively controllingthe direction of operation and dynamic braking of a direct currentmotor,'further comprising:

a second driving circuit for connecting said direct current power sourceacross said first and second armature terminals of said motor to drivesaid motor in a reverse direction, which driving circuit comprises:

a third diode having an anode for connection to said positive side ofsaid direct current power source and a cathode for connection to saidsecond armature terminal,

a a second NPN transistor having a collector for connection to saidfirst armature terminal and an emitter for connection to said negativeside of said direct current power source, and 1 a third resistorconnected'between the base of the second NPN transistor and the cathodeof the third diode,

whereupon, when the third diode cathode is connected to said secondarmature terminal and the second NPN transistor collector is-connectedto said first armature terminal and the second NPN transistor emitter isconnected to 'said negative side of said direct current power source,the connection of the third diode anode to said positive side of saiddirect current power source enables the second NPN transistor to conductthereby completing the second driving circuit to drive said motor insaid reverse direction: and

a second dynamic braking circuit for connection across said armatureterminals of said motor to dynamically brake said driven motor upon thesecond driving circuit being opened so that said armature is coasting inthe reverse direction, which second dynamic braking circuit comprises:

a second PNP transistor having an emitter connected to the cathode ofthe third diode and having a base connected to the anode of the thirddiode,

a fourth diode having an anode connected to the collector of the secondPNP transistor and a cathode connected to the collector of the secondNPN transistor,

a fifth diode having a cathode connected to the collector of the secondNPN transistor, and

a fourth resistor connected between the base of the second PNPtransistor and the anode of the fifth diode,

whereupon when the second driving circuit is connected to said directcurrent power source and to said armature terminals and said motor isbeing driven in said reverse direction, the opening of the seconddriving circuit by disconnecting the anode of the third diode from saidpositive side of said direct current power source to terminateconduction in the second NPN transistor thereby causes the armaturetocoast in the reverse direction to generate electrical energy and alsothereby enables the second PNP transistor to conduct in the dynamicbraking circuit according to claim 1 further response to said generatedelectrical energy to comprises a sixth diode having an anode connectedto the complete the second dynamic braking circuit across collector ofthe PNP transistor and a cathode connected said first and secondarmature terminals; and to the collector of the NPN transistor.

1. A switching circuit for selectively controlling the operation anddynamic braking of a direct current motor having first and secondarmature terminals, comprising: a driving circuit for connecting adirect current power source across said first and second armatureterminals of said motor to drive said motor in a forward direction,which driving circuit comprises; a first diode having an anode forconnection to a positive side of said direct current power source and acathode for connection to said first armature terminal, a NPN transistorhaving a collector for connection to said second armature terminal andan emitter for connection to a negative side of said direct currentpower source, and a resistor connected between the base of the NPNtransistor and the cathode of the first diode. whereupon, when the firstdiode cathode is connected to said first armature terminal and the NPNtransistor collector is connected to said second armature terminal andthe NPN transistor emitter is connected to said negative side of saiddirect current power source, the connection of the first diode anode tosaid positive said of said direct current power source enables the NPNtransistor to conduct thereby completing the driving circuit to drivesaid motor in said forward direction, and a dynamic braking circuit forconnection across said armature terminals of said motor to dynamicallybrake said driven motor upon the driving circuit being opened so thatsaid armature is coasting in said forward direction, which dynamicbraking circuit comprises; a PNP transistor having an emitter connectedto the cathode of the first diode, having a base connected to the anodeof the first diode, and having a collector operatively connected to thecollector of the NPN transistor. a second diode having a cathodeconnected to the collector of the NPN transistor, and a second resistorconnected between the base of the PNP transistor and the anode of thesecond diode, whereupon, when the driving circuit is connected to saiddirect current power source and to said armature terminals and saidmotor is being driven in said forward direction, the opening of thedriving circuit by disconnecting the anode of the first diode from saidpositive side of said direct current power source to terminateconduction in the NPN transistor thereby causes the armature to coast inthe forward direction to generate electrical energy and also therebyenables the PNP transistor to conduct in response to said generatedelectrical energy to complete the dynamic braking circuit across saidfirst and second armature terminals.
 2. A switching circuit according toclaim 1 for selectively controlling the direction of operation anddynamic braking of a direct current motor, further comprising: a seconddriving circuit for connecting said direct current power source acrosssaid first and second armature terminals of said motor to drive saidmotor in a reverse direction, which driving circuit comprises: a thirddiode having an anode for connection to said positive side of saiddirect current power source and a cathode for connection to said secondarmature terminal, a second NPN transistor having a collector forconnection to said first armature terminal and an emitter for connectionto said negative side of said direct current power source, and a thirdresistor connected between the base of the second NPN transistor and thecathode of the third diode, whereupon, when the third diode cathode isconnected to said second armature terminal and the second NPN transistorcollector is connected to said first armature terminal and the secondNPN transistor emitter is connected to said negative side of said directcurrent power source, the connection of the third diode anode to saidpositive side of said direct current power source enables the second NPNtransistor to conduct thereby completing the second driving circuit todrive said motor in said reverse direction: and a second dynamic brakingcircuit for connection across said armature terminals of said motor todynamically brake said driven motor upon the second driving circuitbeing opened so that said armature is coasting in the reverse direction,which second dynamic braking circuit comprises: a second PNP transistorhaving an emitter connected to the cathode of the third diode and havinga base connected to the anode of the third diode, a fourth diode havingan anode connected to the collector of The second PNP transistor and acathode connected to the collector of the second NPN transistor, a fifthdiode having a cathode connected to the collector of the second NPNtransistor, and a fourth resistor connected between the base of thesecond PNP transistor and the anode of the fifth diode, whereupon whenthe second driving circuit is connected to said direct current powersource and to said armature terminals and said motor is being driven insaid reverse direction, the opening of the second driving circuit bydisconnecting the anode of the third diode from said positive side ofsaid direct current power source to terminate conduction in the secondNPN transistor thereby causes the armature to coast in the reversedirection to generate electrical energy and also thereby enables thesecond PNP transistor to conduct in response to said generatedelectrical energy to complete the second dynamic braking circuit acrosssaid first and second armature terminals; and the dynamic brakingcircuit according to claim 1 further comprises a sixth diode having ananode connected to the collector of the PNP transistor and a cathodeconnected to the collector of the NPN transistor.